This invention relates to a naphthalocyanine derivative, a process for producing the same, an optical recording medium using the same, and a process for producing said optical recording medium.
In recent years, it has been proposed to utilize semiconductor laser beams for writing and reading in compact discs, video discs, liquid crystal display devices, optical reading machines, etc. and as light source for electrophotography. For writing or reading by the use of semiconductor laser beams, a substance capable of absorbing semiconductor laser beams, i.e. near infrared rays, is indispensable.
As organic dyes which absorb near infrared rays, cyanine dyes have heretofore been well known, and metal complexes of oximes and thiols and aminated quinone derivatives are also known as dyes absorbing near infrared rays (Yuki Gosei Kagaku Kyokai Shi, vol. 43, page 334 (1985); Shikizai Kyokai Shi, vol. 53, page 197 (1980); Shikizai Kyokai Shi, vol. 58, page 220 (1985).
However, the cyanine dyes have a very low fastness to light, and hence their use has many restrictions. The metal complexes of oximes and thiols are disadvantageous in that the metals are released from the complexes in a certain medium, as the result of which their ability to absorb near infrared rays is lost. The aminated quinone derivatives are disadvantageous in that they are very poor in the ability to absorb near infrared rays.
On the other hand, as materials capable of overcoming these disadvantages, naphthalocyanine derivatives have been disclosed recently. However, conventional unsubstituted metal naphthalocyanines (Zhurnal Obshchei Khimii, vol. 39, p. 2554 (1969) and Mol. Cryst. Liq. Cryst. vol, 112, p. 345 (1984)) are insoluble in organic solvents and hence are very difficult to purify. Recently, synthesis of naphthalocyanine derivatives soluble in organic solvents has been reported (Japanese Patent Application Kokai (Laid-Open) Nos. 60-23451, 60-184565, 61-215662 and 61-215663). However, these naphthalocyanine derivatives have the following disadvantage. That is, although they are generally soluble in aromatic hydrocarbon solvents and halogen-containing solvents, their solubility in saturated hydrocarbon type solvents is quite low, and hence their organic film cannot directly be formed on polymethyl methacrylate and polycarbonate substrates by wet coating process unless a protecting layer is provided on these substrates. Thus, it has been desired to develop a naphthalocyanine compound having an excellent solubility in saturated hydrocarbon type solvents.
Further, they have a problem in that their absorption greatly varies depending on the kind of solvent, concentration, temperature, etc., and in a solution having a high concentration or in the form of a solid film, their ability to absorb semiconductor laser beams is greatly deteriorated, and moreover the reflectance which plays an important role when reflected light is used for reading out information recorded in optical disc is very low in the semiconductor laser region (780-830 nm).
In Japanese Patent Application Kokai (Laid-Open) No. 61-235188, only two compounds are disclosed as naphthalocyanine compounds having a high reflectance, and conception of their synthesis is mentioned in Japanese Patent Application Kokai (Laid-Open) Nos. 61-177287 and 61-177288. However, only a few working examples are presented in these patent gazettes, and only a few compounds can be synthesized in accordance with their descriptions.
Reaction Scheme II (line 3, right upper section, page 8) of Japanese Patent Application Kokai (Laid-Open) No. 61-177288 is a nucleophilic reaction of naphthalocyanine ring resembling Friedel-Crafts reaction and not suitable for introduction of alkoxyl group, alkylthio group and amino group. In reaction Scheme III (line 5, right upper section, page 8) of Japanese Patent Application Kokai (Laid-Open) No. 61-177288, the starting compound cannot be purified and the product is a very complicated mixture difficult to purify, so that this reaction is unsuitable for isolation of high purity product. Further, the reaction itself is disturbed by the influence of hydroxyl group attached to Si of starting compound, and the reaction cannot be advanced toward the intended direction. For the reasons mentioned above, it has been necessary to discover a new synthetic process in order to practically synthesize a new naphthalocyanine compound soluble in saturated hydrocarbon type organic solvent and exhibiting excellent characteristic properties as an optical recording medium, and particularly a naphthalocyanine compound having a sulfur-containing substituent on the naphthalocyanine ring.